Electric discharge apparatus



Dec. 24, 1935.

DOBKE ELECTRIC DI SCHARGE APPARATUS Filed April 1, 19:52

lrn/erdzorz G'u'nther Dobke His fidztowrney- Patented Dec. 24, 1935 UNITED STATES PATENT OFFICE Giinther Dobke, Berlin-Reinickendorf, Germany,

assignor to General Electric Company, a corporation of New York Application April 1, 1932, Serial No. 602,492 In Germany March 31, 1931 3 Claims.

This invention relates to electric discharge apparatus, more particularly to tubes such as lightning arresters which are employed as a protection against abnormal voltages.

.- Tubes of this sort usually contain inert gas at a relatively low pressure and two or more electrodes which are not heated independently of the discharge and hence sometimes referred to as cold electrodes. When used to protect translu mission lines and subject to excessive voltage, induced for example by lightning, an intense discharge may be produced in the tube which tends to be fixed in position and. to concentrate on restricted portions of the electrodes. The dis charge, unless it is moved successively to fresh surfaces of the electrode or caused to spread and distribute itself over the entire surface, may produce pitting, burn-outs or even destruction of the tube.

20 An object of the present invention is to: improve on tubes of this general character with a view to preventing injurious concentration of the discharge under the conditions specified. The improved tube thus has a longer operating life than those of the prior art and is able to withstand higher voltages without breakdown.

This object is attained in brief, by an improvement of the electrode design and arrangement whereby the discharge iscaused to produce a 30 magnetic field which serves to change successively the point of impact of the discharge on the electrode surface or surfaces. Other objects and features will be apparent as the specification is perused in connection with the accompanying 35 drawing. The figure shows an elevational View,

partly in section, of a tube improved in accordance with the present invention.

In the drawing, numeral l designates an evacuated envelope containing an inert gas such as 40 neon or argon, at a relatively low pressure, e. g. 1 mm. to 1 cm. Hg. Within the envelope, there is a. helical electrode 2 and a cylindrical electrode 3, arranged concentrically, one within the other. The member 2 consists of relatively heavy wire 45 of any suitable metal such as copper, nickel or aluminum and. wound in the form of a helix of uniform diameter with the turns barely in contact. The wire preferably is coated with an electron-emitting material such as barium oxide. The

50 ends of the helix may be secured in any suitable manner, as by welding, to a leading-in conductor 4 which is hermetically sealed in the envelope.

The cylinder 3 of metal, which may be similar 55 to the other electrode, is secured to a leading-in conductor 5 sealed in the envelope in any suitable n anner. This cylinder preferably is of greater length than the helix 2 so as to cover a considerable portion of the envelope and to shield the latter as much as possible from electron and 5 positive ion bombardment. The cylinder may also be coated wtih electron-emitting material, if desired.

When a discharge is initiated within the tube as a result of excessive voltage, it has been found that the point of impingement of the discharge with the electrodes continually moves.. While I do not wish to be limited to any theory in this respect, I believe that the movement of the discharge is caused by the magnetic eifect produced in the helix 2 by the current flowing through the tube. The cathode spot has been observed to move along the outer surface of the helix pre-'- sented to the electrode 3 so that all of the turns comprising its surface are successively subjected to the discharge. Consequently, no particular portion of the electrode receives the brunt of the impact for any substantial period of time.

It has further been found that it is not necessary to provide insulation for the turns of the helix other than that afforded by the oxide coat and the small space between the turns. It is apparent that if the device were used in connection with discharges of a direct current character, only one of the electrodes, preferably the helix 2, 80 need be coated with electron-emitting material. However, in the case of lightning discharges which involve alternating current impulses having steep wave fronts, it may be desirable to coat both electrodes.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. An over-voltage protective device comprising an envelope containing inert gas and a plurality of cooperating concentrically arranged electrodes and adapted to be connected to a voltage-protected circuit, one of said electrodes consisting of a helix coated with electronically active material, the. ends of said helix being electrically connected by an equipotential conductor.

2. An over-voltage protective device comprising an envelope containing inert gas and a plurality of cooperating electrodes and adapted to be connected to a voltage-protected circuit, one of said electrodes consisting of a cylinder and 60 another of the electrodes comprising a helix arranged within the cylinder, said helix being coated with electronically active material and having both ends of the helix joined directly to the same leading-in conductor.

3. An over-voltage protective device comprising an envelope containing inert gas at a. pressure between 1 mm. and 1 cm. Hg., a plurality of cooperating electrodes, one of said electrodes consisting of a cylinder and another of the electrodes comprising a helix arranged within the cylinder,

said cylinder being of greater longitudinal length than that 'of the helix, said helix and cylinder being coated with electronically active material and the ends of the helix being electrically connected by an equipotential conductor.

GT'JN'I'HER. DOBKE. 

